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41.
Zeng X Kieffer R Glettner B Nürnberger C Liu F Pelz K Prehm M Baumeister U Hahn H Lang H Gehring GA Weber CH Hobbs JK Tschierske C Ungar G 《Science (New York, N.Y.)》2011,331(6022):1302-1306
T-shaped molecules with a rod-like aromatic core and a flexible side chain form liquid crystal honeycombs with aromatic cell walls and a cell interior filled with the side chains. Here, we show how the addition of a second chain, incompatible with the first (X-shaped molecules), can form honeycombs with highly complex tiling patterns, with cells of up to five different compositions ("colors") and polygonal shapes. The complexity is caused by the inability of the side chains to separate cleanly because of geometric frustration. Furthermore, a thermoreversible transition was observed between a multicolor (phase-separated) and a single-color (mixed) honeycomb phase. This is analogous to the Curie transition in simple and frustrated ferro- and antiferromagnets; here spin flips are replaced by 180° reorientations of the molecules. 相似文献
42.
Mobilization of non‐exchangeable ammonium (NH ) by hyphae of the vesicular‐arbuscular mycorrhizal (VAM) fungus Glumus mosseae was studied under controlled experimental conditions. Maize (Zea mays) and parsley (Petroselinum sativum) were grown either alone or in symbiosis with Glomus mosseae in containers with separated compartments for roots and hyphal growth. In one experiment, 15NH was added to the soil to differentiate between the native non‐exchangeable NH and the non‐exchangeable NH derived from N fertilization. Non‐exchangeable NH was mobilized by plant growth. Plant dry weight and N uptake, however, were not significantly influenced by mycorrhizal colonization of the roots. The influence of root infection with mycorrhizal fungus on the mobilization of non‐exchangeable NH was negligible. In the hyphal compartment, hyphal uptake of N resulted in a decrease of NH in the soil solution and of exchangeable NH . However, the NH concentration was still too high to permit the release of non‐exchangeable NH . The results demonstrate that, in contrast to roots, hyphae of VAM fungi are not able to form a non‐exchangeable‐NH depletion zone in the adjacent soil. However, under conditions of a more substantial depletion of the exchangeable NH in the mycorrhizal sphere (e.g., with longer growth), an effect of mycorrhiza on the non‐exchangeable NH might be found. 相似文献
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44.
Industrial activities in the river basin of the Elbe have a very long tradition, and have been resulting in the contamination
of sediments for centuries. Contamination lasted until the fall of the iron curtain; since then, the situation has improved
significantly. In the transition zone between freshwater systems and the marine environment, ports like Hamburg still have
to bear this burden of history. An overall (contaminated) management strategy should be developed in the context of the European
Water Framework Directive with the emphasis on source control.
Axel Netzband gave a keynote lecture during the SedNet Inaugural Conference, April 22–24, 2002, which forms the basis of this
article. 相似文献
45.
Quantitative estimation of the mineralogical composition of silt fractions of soils based on both, chemical analysis and application of Karl-Fischer-titration. I. Method This paper describes a method for calculating the mineralogical composition of the silt fractions of soils. The chemical analysis and the temperature dependence of water release are used for determining micas and feldspars, each in three components in a relatively short procedure. The release of water was measured by Karl-Fischer-titration at controlled temperatures. At temperatures above 550°C the water release of the particle size fractions correlates with their content of micas. The quantity of micas can be obtained from the amount of released water and the results of the chemical analysis. The influence of kaolinite, amphibole and the fluoride content on the calculation is described. By considering the potassium content of the mica fraction results of the chemical analysis are used to quantify feldspars. 相似文献
46.
A sensitive bioassay method was developed using bidirectional diffusion of fungicides in agar bands instead of diffusion through 360°. This method permitted the measurement of fungicide movement through isolated cuticular disks into agar bands underneath. Oil dispersible formulations of oxycarboxin and pyracarbolid penetrated through cuticles of coffee much more efficiently than wettable powder formulations. 相似文献
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48.
Heinrich Buchenauer 《Pesticide biochemistry and physiology》1977,7(4):309-320
Triadimefon [1-(4-chlorophenoxy)-3,3-dimethyl-(1,2,4-triazol-1-yl)-2-butanone], 1.5–2.0 μ/ml, inhibited the multiplication of sporidia of Ustilago avenae more strongly than it did the increase of dry weight. The treated sporidia appeared swollen, multicellular, and branched. At concentrations of 1.5–100 μg of triadimefon/ml, the oxidation of glucose was not affected. Increase in dry weight and synthesis of protein, RNA, and DNA were inhibited slightly, whereas cell division was acutely arrested. After an incubation period of 9.5 hr, microscopic studies revealed that daughter cells of the treated sporidia also contained one nucleus. In sporidia treated for 6 hr with triadimefon, both the total lipid content and its composition of fatty acids were not appreciably altered. The treated cells, however, differed from control cells by a higher content of free fatty acids. Triadimefon markedly interfered in sterol biosynthesis in Ustilago avenae. Gas chromatographic (glc) analysis and [14C]acetate incorporation studies indicated that ergosterol biosynthesis was almost completely inhibited by triadimefon; on the other hand, sterol compounds representing precursors of ergosterol (probably 4,4-dimethyl and C-4-methyl sterols) accumulated in treated sporidia. As the results indicate, the inhibition of conversion of immediate sterol precursors to ergosterol may be regarded as the primary target for the action of triadimefon in Ustilago avenae. 相似文献
49.
50.
Heinrich C 《The Veterinary record》2005,156(23):750; discussion 750-750; discussion 751